I use restic and Backblaze B2 for offline backup storage at a cost of $6/TB/month. I don't backup my entire ~20TB NAS and its datasets however, so I'm only paying about ~$2/month right now. I only backup the most important things I cannot afford to lose or annot re-created.

@movq From what I can tell, they use strict semantic versioning and backwards compatibility. There are two versions of the storage, v1 and v2, but it doesn't look like v2 is enabled yet.